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Ferroelectricity of polycrystalline GdMnO3 and multifold magnetoelectric responses L. Lin · L. Li · Z.B. Yan · Y.M. Tao · S. Dong · J.-M. Liu

Received: 20 May 2012 / Accepted: 16 November 2012 © Springer-Verlag Berlin Heidelberg 2012

Abstract The multiferroic behaviors of polycrystalline GdMnO3 are investigated by focusing on the ferroelectric response to the spin ordering sequence and external magnetic field. The polarization current shows sensitive response to both the Mn cycloidal spin order and Gd antiferromagnetic (AFM) order. The complicated magnetoelectric behaviors suggest that the Mn cycloidal spin order can be modulated by the Gd AFM order at low temperature via the Gd–Mn spin interaction. Due to the possible disorder and defects in polycrystalline nature, polycrystalline GdMnO3 may accommodate the cycloidal spin order in addition to the A-type AFM order at Mn sites, as illustrated by simulation based on the two-orbit double exchange model and measured hysteresis loops of polarization against magnetic field, indicating the switching of the ferroelectric domains coupled with the magnetic domains in response to magnetic field.

1 Introduction Type II multiferroics, in which magnetic and ferroelectric (FE) orders couple intrinsically, have been retrieving speL. Lin · L. Li · Z.B. Yan · Y.M. Tao · J.-M. Liu () Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China e-mail: [email protected] L. Li · J.-M. Liu Institute for Advanced Materials, South China Normal University, Guangzhou 510006, China S. Dong Department of Physics, Southeast University, Nanjing 211189, China

cific attentions recent years not only for promising technological potentials but more from fundamental research interests [1–4]. The major advantage of type II multiferroics is the interactive control of FE polarization (P ) (magnetization M) by magnetic field H (electric field E). Since the discovery of such an effect in TbMnO3 [5], a number of complex transition metal oxide multiferroics have been synthesized and the major physics underlying these materials is being unveiled [6–12]. One of the common features in these multiferroics is that P arises from specific spin orders via spin-correlated mechanisms, in particular in noncollinear cycloidal spin (CS) order via the inverse Dzyaloshinskii–Mariya interaction mechanism (asymmetrical exchange striction) [13, 14] or E-type antiferromagnetic (E-AFM) order via the symmetric exchange striction [15, 16]. The representative multiferroics to illustrate above phenomena go to orthorhombic perovskite rare-earth manganites RMnO3 (Pbnm symmetry). Upon decreasing R-site ionic size (RA ), the Mn spin order evolves from A-type antiferromagnetic (A-AFM) order (R = La to Gd) to CS order (R = Tb and Dy) and eventually toward E-AFM order (R = Ho and smaller), due to the competing spin interactions associated with distorted GdFeO3 -type lattice including the Jahn–Teller active distortion [17]. For the CS order and E-AFM order, large P and gigantic magnetoelectric (ME) effect were